utf8_to_uv_msgs: Silence some compiler warnings

These showed up running gcc on a 32-bit build

utf8.c

@@ -1765,7 +1765,7 @@ Perl_utf8_to_uv_msgs_helper_(const U8 * const s0,
      * there are other malformations, we may be still be able to tell if this
      * is an overlong by looking at the UTF-8 byte sequence itself */
     if (   (   LIKELY(! possible_problems)
-            && UNLIKELY(expectlen > OFFUNISKIP(uv)))
+            && UNLIKELY(expectlen > (SSize_t) OFFUNISKIP(uv)))
         || (   UNLIKELY(possible_problems)
             && UTF8_IS_SYNTACTIC_START_BYTE(s0)
             && UNLIKELY(0 < is_utf8_overlong(s0, s - s0))))
@@ -1841,7 +1841,7 @@ Perl_utf8_to_uv_msgs_helper_(const U8 * const s0,
                  * full length with occurrences of the smallest continuation
                  * byte.  For surrogates we could just look at the bytes, but
                  * this single algorithm works for both those and supers. */
-                for (unsigned i = curlen; i < expectlen; i++) {
+                for (int i = curlen; i < expectlen; i++) {
                     uv = UTF8_ACCUMULATE(uv, UTF8_MIN_CONTINUATION_BYTE);
                 }
             }
@@ -2073,7 +2073,8 @@ Perl_utf8_to_uv_msgs_helper_(const U8 * const s0,
             switch (this_problem) {
               default:
                 Perl_croak(aTHX_ "panic: Unexpected case value in "
-                                 " utf8n_to_uvchr_msgs() %d", this_problem);
+                                 " utf8n_to_uvchr_msgs() %ld",
+                                 (long) this_problem);
                 /* NOTREACHED */
                 break;